A blog about search, search skills, teaching search, learning how to search, learning how to use Google effectively, learning how to do research. It also covers a good deal of sensemaking and information foraging.

In this paper, the authors argue that a large eruption
flooded the area around the Great Pyramid on Cholula with lahar outflows.(Remember that lahars are rivers of superhot
mud, rocks, and generally nasty stuff that can travel up to 50 miles from the
original volcano at speeds of up to 90 mph.

If you look at Figure 1 from their paper, it's clear they think the Pyramid was hit by the lahars:

As the authors write:

"Our investigations
indicate that a major cataclysmic eruption occurred at Popocatépetl at about
this time, affecting a minimum area of
3000 km^2. In addition to the volcanic hazards associated with the base
surges, pumice falls, and ash flows, widespread volcanic mudflows reached the
base of the great pyramid of Cholula (Figs. 1 and 3). The sequence of volcanic
mudflow deposits is several metres thick and contains abundant pumice, pottery
shards, obsidian artifacts, and carbon. Carbon from this sequence at Cholula
yielded an age of A.D. 790 (+/-
175)."

Siebe, C., & Macías, J. L. (2006). “Volcanic hazards in
the Mexico City metropolitan area from eruptions at Popocatépetl, Nevado de
Toluca, and Jocotitlán stratovolcanoes and monogenetic scoria cones in the Sierra
Chichinautzin Volcanic Field” SPECIAL PAPERS-GEOLOGICAL SOCIETY OF AMERICA,
402, 253.

But it’s interesting to note that the text used to describe
the 822 AD lahars reaching the foot of the Great Pyramid in Cholula is exactly the same each time (suggesting
that the text was simply copied from paper to paper without any newer
data).

Then there is additional work that agrees with this that
we’ve already found.

The downside of this web document is that it’s just a note,
not an official publication.There are
no references, etc.But it seems
reasonably believable.As we see, the
author comes from a credible institution and has good credentials in this
area.

ON THE OTHER HAND…

Fred wrote in with an intriguing comment in the stream:

Google Search [ Popocatepetl
caldera formed ] and find a book "Geology of México: Celebrating the
Centenary of the Geological Society of México" pp 199-201 Page 201 has a
great timeline/stratigraphic image of past eruptions.

I go back and try to find another
source for flow reaching the pyramid [ pyramid cholula 850..700 lahar ] but the
range search but the range search doesn't appear to work in reverse, so [
pyramid cholula 700..850 lahar ] to and discover the Mesoamerican Research
Foundation.

The Google Quick Scroll extension
leads me to this passage: "NOTE: Beginning in 1993, scientific studies
find that volcanic activity has produced several eruptions, two of which were
the most violent. The first was, ''at the beginning of the present era'' or
first century A.D. The second was, ''between A.D. 700 and 850.'' (Plunket &
Urunuela 1998)."

I repeated Fred’s search for [ Plunket & Urunuela 1998 ]
and found the PDF for the paper.

Plunket, P., and G. Uruñuela. "Mountain of sustenance,
mountain of destruction: The prehispanic experience with Popocatépetl
volcano." Journal of Volcanology and Geothermal Research 170.1
(2008): 111-120.

This paper talks about the artifacts and radiocarbon dating of
artifacts found at the site suggesting they were covered sometime between
700-900AD.

But one of the key points made in this paper is that:

“...a zone that
should show the presence of these deposits if indeed they reached the Pyramid –
to date have failed to find stratigraphic evidence of these lahars (López et
al., 2002a,b; Plunket and Uruñuela, 2002b, 2005a,b).”

Later in that paper, the authors write:

“Excavations on the campus of the Universidad de las
Américas to the east of the Great Pyramid have demonstrated that, in areas
where stratigraphy is intact, lahar deposits are also absent
although a sterile layer of sandy volcanic ash consistently seals the black
clay deposits of the Classic period; cultural materials overlying this layer
belong to the Early Postclassic (Plunket and Uruñuela, 2005b,
p.103)."

SO… What have we found here?

We’ve found that the story isn’t quite as cut and dried as I
thought.

The Siebe crowd believes that the evidence is quite clear
that the lahar flow of ca. 800 AD reached the based of the Great Pyramid.The Plunket crowd disagrees.

We are in the middle of an old-fashioned scientific
disagreement, with evidence being mounted on both sides.

I’ve spent about 8 hours quite happily reading through the
literature of volcanoes and archaeology in the area of Puebla and Colula.It’s been hugely fun, but in the end, both
groups are arguing about whether or not the lahars made it all the way to the
Pyramid or not.

A big problem for the Plunket argument is the some of the
basic work is not generally available.Here’s a citation that’s given:

And so it goes, back and forth.Plunket (an archaeologist) disagrees with
Siebe’s (the geologist) interpretation of what’s seen at the pyramid site.Is it a mud flow from the volcano?Or just the melting of adobe bricks over the
years down onto the plain?

I don’t think we’re going to be able to figure this out by
just web searches.This is really a case
where we now understand that there is evidence for, and evidence against.We could read through all of the literature
and make a reasoned guess at the evidence, but that’s the job of a geology (or
archaeology) graduate student.

Note that this kind of conversation happens ALL the time in
the Talk pages of Wikipedia.You can see
this even in something as innocuous as the Wikipedia page on Chocolate.If you read the “Talk” page for Chocolate, you’ll see an animated debate about what should go into the article on
chocolate, even reaching into politically charged topics such as child
slavery!

And, of course, this kind of open debate about evidence and
conclusions is just the normal operation of science. Even in fields where the “standard
interpretation” would seem to be fairly stable, new interpretations arise,
sometimes by people from outside of the field.
See, for instance, Nathan Myhrvold’s critique of growth rate data in
dinosaurs in which he questions the well-accepted data and analysis of how quickly dinosaurs grew. (NY Times article) and his own publication site, which reprints an article he authored in PLOS One (a fairly respected online
with peer reviewed articles, but are not excluded on the basis of lack of
perceived importance or adherence to a scientific field).

FWIW, I first saw this in the NYTimes Magazine (“A team of Belgian
doctors recently confirmed the existence of a new ligament in the human
knee…”)12/8/13, and when I checked on
it, the story had pretty clearly been blown up out of proportion.

Search lesson:Overall, then, the key search lesson from
our Popo adventure is that it’s well worth looking around a bit more after
finding your initial result. Discoveries are often not what you think when they're first noted. Subsequent articles frequently update recieved knowledge. Hint: Look for variationsin the answers; and sometimes, just
sometimes, you stumble into a very fun debate.And we realize once more that not all of science and history is quite as
locked-down we'd thought. Sometimes you really have to go beyond just a simple lookups of facts.

MANY THANKS to the SearchResearchers who pointed out the alternative interpretations of the "lahar" flows around the Great Pyramid in Cholula. Special shout-out to Ramón and Fred, who went the extra mile to contact the authors of some of these reports and dig more deeply into the topic.

1 comment:

I needed a break. I saw on Dr. Oz this new ligament discovery you mention and you can watch the video with animation discussing the A.L.L. and not the A.C.L. I listened closely and my impression is they say new discovery but it has more to do with doctors realizing they should look at the A.L.L. for knee injuries. I will check out NY Times articled.